1. Field of the Invention
This invention relates to an autofocus apparatus, and more particularly to an autofocus apparatus in which a focusing lens is moved to automatically conduct a focusing operation so as to maximize the high frequency component included in an object image signal produced by an imaging means.
2. Description of the Prior Art
There is known an automatic focusing method in which a focusing operation is conducted automatically by extracting a high frequency component from an object image signal produced by an imaging means (for example, a TV camera or the like) and moving a focusing lens so as to maximize the extracted high frequency component.
However, this automatic focusing method in which a focusing operation is conducted automatically by extracting a high frequency component from an object image signal produced by an imaging means (for example, a TV camera or the like) and moving a focusing lens so as to maximize the extracted high frequency component entails the problem that when the object or the camera moves, the high frequency component contained in the image signal becomes smaller, just as if the focus condition had changed. As a result, the automatic focusing operation commences in spite of the fact that the focus condition is proper, so that the picture on the monitor TV first goes out of focus and then back into focus, which is highly unpleasant to the viewer. Further, when the object is outside the focus range of the focusing lens, the automatic focusing operation is repeated endlessly because no determination that the focused state has been obtained can be made no matter how long the operation continues.